In four years time, I'm planning on being in California, as I make my way around the world by bicycle. As I pass through California, I'm wanting to do a bit of railfanning along BNSF's Cajon Subdivision - specifically between Hesperia and Keenbrook (I already have Tehachapi, et al, sorted out). Does anyone have any information on bicycle accessible roads/tracks through there?

Yeah, I might do that. I sent an email off to Pentrex, in regards to their shooting locations used for The Ultimate Cajon Subdivision. Unfortunately, when Highball took them over, none of their records went with them.